RU2624619C2 - Device for determining manganite concentration of rare-earth elements - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: device for determining manganite concentration of rare-earth elements (MREE) consists of a light source - a mercury lamp, a light source power supply unit, a light rays photodetector, a photodetector power supply unit, a microvoltmeter for measuring the photodetector current. The device also includes a set of light filters which allows only the transmission of emission line of mercury lamps with a wavelength of 546 nm on the study sample. The concentration of the specific studied MREE is determined by the reflection coefficient value at 546 nm wavelength and the previously obtained dependence of the reflection coefficient on the manganite concentration of rare-earth elements.

EFFECT: possibility of measuring the manganite concentration of rare-earth metals.

3 dwg

Description

To determine the concentration of compounds in the solid phase, there are several methods based on various physical processes. The most common is x-ray phase analysis (XRD), carried out using x-ray diffractometers. With this method, the concentration of compounds in the test material is determined by the intensity of x-rays reflected from various nodes of the crystal lattices of this material as a whole or its components [1].

Another method for directly determining the concentration of compounds in the solid phase is secondary ion mass spectrometry (SIMS). With this method, the concentration of the compounds contained in the test material is determined by the intensity of the peaks in the mass spectra corresponding to the elements included in these compounds. The studied material in SIMS installations is sprayed in a vacuum with a beam of ions (most often inert gas ions) and the types and concentration of atomized atoms, molecules or conglomerates are analyzed using a mass spectrometer [2].

The next way to directly determine the concentration of compounds in the solid phase is Auger electron spectroscopy, based on the effect discovered in 1925 by the French scientist Auger. The effect is the emission of electrons (in addition to quanta) during the transition of electrons from high electron shells to lower ones in an atom. Since each chemical element has its own system of electron shells, the types and concentration of elements in the analyzed material are determined by the distribution of recorded electrons by energy using energy analyzers, and by the concentration of electrons recorded using microammeters [3].

Known and widely used spectrophotometric method for determining the concentration of compounds in the solid phase. It consists in placing a given compound in a liquid, measuring the transmission spectra of both the liquid itself and the solution with this compound. From the obtained values of the transmittance at certain wavelengths, the optical density is calculated, and a graphical dependence of the optical density on the concentration of the compound is built. Then, according to this dependence, for a particular substance, the concentration value is determined by the results of optical density measurements [4].

To implement this method, a spectrophotometer is required, including a monochromator, diffraction gratings, a light source and a photodetector for the required range of the spectrum, power supplies for the light source and photodetector, a microammeter for measuring the photodetector current. The most expensive element of a spectrophotometer is a monochromator.

If a synthesized or natural compound contains several components - a mixture of components, then to determine the concentration of each component in this way, calibration must be carried out for each component in a specific spectral region or at a specific radiation wavelength. Then, comparing the graduations for each component, determine their concentration. This method is selected as a prototype.

The reflection spectra of manganites of rare-earth elements are such that in the region of 500-600 nm a minimum reflection coefficient is recorded (Fig. 1), due to the absorption band of electrons (transitions Mn ⁴⁺ → Mn ³⁺ ) during the formation of solid solutions of the type LaMnO ₃ , LaSrMnO ₃ , LaCaMnO ₃ [5, 6]. The magnitude of the dip - the value of the reflection coefficient is a characteristic of the concentration of MRE compounds. Therefore, by recording the value of the reflection coefficient in this region, one can determine the concentration of MRE from the calibration curve.

In the proposed method for determining the concentration of manganites of rare-earth elements (MRE), as in the prototype, a light source and a photodetector for the required range of the spectrum, power supplies for the light source and photodetector, a microvoltmeter for measuring the photodetector current are used. Unlike the prototype, instead of an expensive monochromator with diffraction gratings designed to isolate radiation of a certain wavelength for the purpose of recording the spectrum, a mercury lamp with a linear emission spectrum and a set of three glass filters are used to cut (remove) all emission lines except line 546 nm Such a set may include OS-11, PS-7, and SZS-21 filters.

The aim of the invention is a device containing all of the listed circuit elements with the exception of the monochromator. A diagram of the device is shown in FIG. 2, the operation of which is that a voltage is supplied to the RL mercury lamp from the BP-1 power supply, the light emitted by the lamp in separate lines falls on a set of SF filters, consisting of OS-11, PS-7 and SZS-21 filters, in which all emission lines are cut except for the 546 nm line. This radiation passes through the focusing lens L1 to the sample O. The beam reflected from the sample is directed to the focusing lens L2 and then to the photodetector in the visible spectral range of the type FEU-74, or FEU-118, or FEU-176, which is powered from the PSU -2. The PMT current detected by the MkV microvoltmeter in the form of a voltage drop across the calibration resistance is proportional to the intensity of a light beam with a wavelength of 546 nm and the reflection coefficient of the MRE sample under study. The value of the reflection coefficient using the calibration dependence determines the concentration of REE in the test sample.

To obtain the dependence of the concentration of MRE compounds on the reflection coefficient at a wavelength of 546 nm, experimental studies were performed. For this, in various synthesis modes (temperature and heating time, concentration of strontium ions), various concentrations of the rare-earth element LaSrMnO _{3 were} obtained. The concentration of LaSrMnO _{3 was} determined by XRD on a Shimadzu XRD 6000 X-ray diffractometer, the reflection coefficient at a wavelength of 546 nm with a Perkin Elmer Lambda 950 spectrophotometer. The dependence of the reflection coefficient at a wavelength of 546 nm on the concentration of the LaSrMnO ₃ compound, which turned out to be linear, was constructed (Fig. 3). According to this dependence, by measuring the value of the reflection coefficient at a wavelength of 546, one can determine the concentration of MRE in various powders, ceramics, or natural minerals.

Information sources

1. Physical methods for the study of inorganic substances / Ed. A.B. Nikolsky. M .: Academy, 2006, 444 p.

2. Mikhailov M.M. Radiation and space materials science. Tomsk University Press, Tomsk, 2008, 440 p.

3. Z. Marchenko, M. Balcezak. Spectrophotometric methods in UV and visible regions in inorganic analysis. Per. with the floor. A.V. Garmash. Publisher: Binom Laboratory of Knowledge, 2009, 711 p.

4. Carlson T. Photoelectron and Auger spectroscopy, trans. from English., L., 1981; Electronic and ion spectroscopy of solids. / per. from English, ed. IN AND. Rakhovsky, M., 1981. 435 p.

5. G. Tang, Y. Yu, Y. Cao and W. Chen, The thermochromic properties of Lal-xSrxMnO3 compounds, Solar Energy Materials & Solar Cells, vol. 92, pp. 1298-1301, 2008.

6. K. Takenaka, K. Iida, Y. Sawaki, S. Sugai, Y. Moritomo and A. Nakamura, Optical Reflectivity Spectra Measured on Cleaved Surfaces of Lal-xSrxMnO ₃ : Evidence against Extremely Small Drude Weight, Journal of the Physical Society of Japan, vol. 68, pp. 1828-1831, 1999.

Claims (1)

A device for determining the concentration of rare-earth manganites by a spectrophotometric method, including a light source - a mercury lamp, a light source power supply, a photodetector for the visible spectral region of the type ФЭУ-74, or ФЭУ-118, or ФЭУ-176, a photodetector power supply, a microvoltmeter for measuring current photodetector, characterized in that a set of optical filters of the OS-11, PS-7 and SZS-21 type is used, which ensures that only the emission line of mercury lamps with a wavelength of 546 nm, necessary for measuring reflection the coefficient, which is proportional to the concentration of rare earth manganites.

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